High Cu(I) and low proton affinities of the CXXC motif of Bacillus subtilis CopZ

Liang Zhou , Chloe Singleton , Nick E Le Brun (1)

1 School of Chemical Sciences and Pharmacy

CopZ, an Atx1-like copper chaperone from the bacterium Bacillus subtilis, functions as part of a complex cellular machinery for Cu(I) trafficking and detoxification, in which it interacts specifically with the transmembrane Cu(I)-transporter CopA. Here we demonstrate that the cysteine residues of the MXCXXC Cu(I)-binding motif of CopZ have low proton affinities, with both exhibiting pKa values at 6 or below. Chelator competition experiments demonstrated that the protein binds Cu(I) with extremely high affinity, with a small but significant pH-dependence over the range pH 6.5 – 8.0. From these data, a pH-corrected formation constant, β2 = ~6 × 1022 M-2, was determined. Rapid exchange of Cu(I) between CopZ and the Cu(I)-chelator BCS indicated that the mechanism of exchange does not involve simple dissociation of Cu(I) from CopZ (or BCS), but instead proceeds via the formation of a transient Cu(I)-mediated protein-chelator complex. Such a mechanism has similarities to the Cu(I)-exchange pathway that occurs between components of copper trafficking pathways.

Mots clés: Life Sciences

Liang Zhou, Chloe Singleton, Nick E Le Brun. High Cu(I) and low proton affinities of the CXXC motif of Bacillus subtilis CopZ. Biochemical Journal, 2008, 413 (3), pp.459-465. ⟨10.1042/BJ20080467⟩. ⟨hal-00478990⟩